(1) Field of the Invention
The present invention relates to a snowmobile equipped with a four-cycle engine, in particular relating to an intake structure of a snowmobile engine.
(2) Description of the Prior Art
Conventionally, most snow vehicle such as snowmobiles and the like use two-cycle engines, which are relatively simple in structure, light and compact and yet powerful. Recently, however, because of regulation of exhaust gas or aiming at improvement of fuel consumption, there is a trend toward employing four-cycle engines. In contrast to two-cycle engines, which are compact and high in power, four-cycle engines need a camshaft and oil lubrication, inevitably tending towards large size.
Therefore, it is necessary to provide a contrived layout of the oil pan configuration, intake and exhaust systems and associated auxiliaries, in order to make the body and engine hood of a snowmobile equipped with a four-cycle engine having a similar size to that of a two-cycle engine.
In general, in order to improve the maneuverability of a snowmobile, it is preferred that the engine should be set as low as the steering tie-rod so that the center of gravity of the vehicle with the engine mounted is positioned at a low position while the engine should be set as close to the steering post as possible so that the center of gravity will be set at the center of the body.
Now, consider a configuration where the engine of an existing two-cycle snowmobile is replaced with a four-cycle engine and the crank center of the four-cycle engine is set at the same position as that of the original two-cycle engine. In this case, since a four-cycle engine has an oil pan at its bottom, it has a greater height than the two-cycle engine. Therefore, if the engine is arranged with its cylinders set upright, in some cases the engine may interfere with the steering rod, or in other cases the cylinder head and throttle body may interfere with the engine hood.
Further, the two-cycle snowmobile engine needs a large capacity expansion chamber for improving the performance. This chamber is generally routed on the side opposite to the drive clutch and connected to the muffler. The reason the exhaust system is thus laid out can be attributed to the necessity of providing a space for routing and for adjusting the weight balance between the left and right. A flywheel magneto, the chamber and muffler are arranged on the side opposite to the clutch which is heavy.
Electronic and electric parts such as an engine control unit (ECU), capacitive discharge ignition (CDI) unit and the like are attached on the top of the air cleaner, to the chassis or the engine in order to avoid breakage from vibrations.
However, if these electronic and electric parts are disposed away from the engine, the wires have to be tied up or clamped which is unpreferable from the viewpoint of layout.
A model with a starter motor needs a battery for electric supply, and the battery is usually disposed away from the clutch and muffler. Therefore, it is some distance from the engine so the lead wires have to be routed and clamped.
If the exit of the muffler is arranged near the rider, the noise becomes too large and harsh to the ear. If the exit of the muffler is offset to one side, either left or right, the exhaust noise during travel differs between the left and right of the vehicle, causing a noise problem.
Further, since snowmobiles are used in cold areas, there is a fear that the breather hose for releasing the pressure inside the head cover may be frozen because oil mixed with water circulates through the breather hose. Once it is frozen, the pressure inside the head cover increases, causing sealing deficiencies and lowering the power. Moreover, since snowmobiles travel on undulating courses, there is a fear that oil may leak out from the breather as the body moves to and fro.
The present invention has been devised in view of the above prior art problems, it is therefore an object of the present invention to provide a snowmobile equipped with a four-cycle engine, in which the four-cycle engine can be mounted with its center of gravity at a position low enough without interference with the engine hood, and which is improved in travelling performance by setting the centroid of the engine close to the centroid of the snowmobile body and lowering the center of gravity.
It is another object of the present invention to provide a four-cycle engine which is reduced in exhaust noise therefrom.
It is a further object of the present invention to provide an intake structure for a snowmobile engine, which is able to prevent oil leakage when the snowmobile body is tilted and which is able to prevent freezing inside the intake passage.
In order to achieve the above objects, the present invention is configured as follows:
In accordance with the first aspect of the present invention, a snowmobile having a four-cycle engine mounted on a front body thereof and enclosed by an engine hood located in front of a seat is characterized in that the four-cycle engine is mounted in such a manner that the crankshaft is arranged along the body width direction and the central axis of a cylinder(s) is tilted rearward with respect to the vertical direction of the snowmobile body, forming a rear tilted engine; at least part of the engine intake system including an air cleaner box and throttle body, located over the engine and connected to the intake port(s) at the rear part of the cylinder head is accommodated in the topmost space of the engine hood; and exhaust is led out to the front of the cylinder(s) by an exhaust system connected to the exhaust port(s) of the front part of the cylinder head.
In accordance with the second aspect of the present invention, the snowmobile equipped with a four-cycle engine, having the above first feature is characterized in that the engine hood has an upward projected portion formed at top thereof, a headlight is disposed at the front of the projected portion and an instrument panel for indicating the condition of the vehicle at the rear of the projected portion, and at least part of the intake system is accommodated in the space sandwiched between the headlight and instrument panel in the projected portion.
In accordance with the third aspect of the present invention, the snowmobile equipped with a four-cycle engine, having the above first feature is characterized in that the exhaust system includes an exhaust manifold connected to the exhaust port(s) at the front of the cylinder head and an exhaust muffler located in front of the engine and connected to the exit of the exhaust manifold by an exhaust pipe, both being arranged inside the engine hood, and the exhaust system further has an exhaust lead path from the muffler, with an opening formed in the body bottom at the center with respect to the body width so that exhaust will be discharged from the opening to the outside of the snowmobile body.
In accordance with the fourth aspect of the present invention, the snowmobile equipped with a four-cycle engine, having the above third feature is characterized in that the muffler is arranged at a level lower than the engine cylinder(s) and the exhaust pipe from the exhaust manifold is extended frontwards and downwards to the muffler.
In accordance with the fifth aspect of the present invention, the snowmobile equipped with a four-cycle engine, having the above third feature is characterized in that the muffler is of an overally cylindrical shape with its cylinder axis directed along the body width, and exhaust from the engine is led into the muffler via an exhaust pipe that is connected to the muffler at one side with respect to the body width.
In accordance with the sixth aspect of the present invention, the snowmobile equipped with a four-cycle engine, having the above first feature is characterized in that the four-cycle engine is arranged in the engine hood so that the lengthwise center of the crankshaft is off-centered to one side with respect to the center of the body width.
In accordance with the seventh aspect of the present invention, the snowmobile equipped with a four-cycle engine, having the above sixth feature is characterized in that, in the engine hood, a clutch mechanism is arranged on one side, with respect to the body width, of the engine while a battery is disposed on the other side with respect to the body width.
In accordance with the eighth aspect of the present invention, the snowmobile equipped with a four-cycle engine, having the above seventh feature is characterized in that electrical equipment is attached to a battery holder for mounting the battery.
In accordance with the ninth aspect of the present invention, an intake structure of an engine for a snowmobile wherein a four-cycle engine positioned with its cylinder head at the upper side is provided at the approximate center of an engine room formed in the front body thereof, a steering post equipped with a steering device at the top end thereof for maneuvering the snowmobile is set up in the engine room so that it stands with its steering device side tilted to the rear, is characterized in that the engine is arranged in front of the steering post and an intake passage is disposed between the steering post and the engine body.
In accordance with the tenth aspect of the present invention, the intake structure of a snowmobile engine, having the above ninth feature is characterized in that an intake manifold constituting part of the intake passage is arranged at the side of the steering post in such a manner that air is supplied to the manifold by downdraft ventilation.
In accordance with the eleventh aspect of the present invention, the intake structure of a snowmobile engine, having the above ninth feature is characterized in that the front body includes an instrument panel at the top and an engine hood in front of the instrument panel, and the engine hood is formed so that it starts at a position stepped down a degree from the front end of the instrument panel toward the front end while a headlight facing outwards and frontwards is arranged at the stepped portion between the engine hood and instrument panel, and a carburetor constituting part of the intake passage is disposed in a space behind the headlight under the instrument panel inside the engine room.
In accordance with the twelfth aspect of the present invention, the intake structure of a snowmobile engine, having the above ninth feature is characterized in that the engine is arranged so that the axis of its crankshaft therein is oriented approximately parallel to the body width direction while the carburetor is positioned at a level higher than the cylinder head.
In accordance with the thirteenth aspect of the present invention, the intake structure of a snowmobile engine, having the above ninth feature is characterized in that the engine includes an air cleaner box disposed at the rear of a head cover that covers the cylinder head and a first breather hose that connects the interior of the head cover with the interior of the air cleaner box, and the first breather hose is connected at one end to the rear side of the head cover on the drive-clutch side and is extended approximately linearly, and parallel to, the axial direction of the crankshaft, from the drive clutch side to the opposite side and bent perpendicularly, when viewed from top, and further extended and connected at the other end to the air cleaner box.
In accordance with the fourteenth aspect of the present invention, the intake structure of a snowmobile engine, having the above thirteenth feature is characterized in that, when the snowmobile body is in its horizontal position, the first breather hose is positioned so that a joint to head cover is lower than another joint to the air cleaner box.
In accordance with the fifteenth aspect of the present invention, the intake structure of a snowmobile engine, having the above ninth feature is characterized in that the engine includes a second breather hose for connecting the interior of the air cleaner box to the outside of the snowmobile body, and the second breather hose is connected at one end to the bottom of the air cleaner box and the other end is arranged penetrating through the bottom of the front body and opening to the outside, whereby the water inside the air cleaner box is drained to the outside of the body.
According to the present invention, since the four-cycle engine is tilted rearwards so that part of the intake system over the engine can be accommodated on the rear side of the headlight inside the topmost portion of the engine hood, it is possible to avoid its interference with the engine hood and headlight and yet markedly reduce the full height of the engine compared to the configuration where the engine is mounted in its upright position. Further, the rear tilt arrangement of the four-cycle engine in the engine hood of the front body makes the center of gravity of the engine close to the center of the body and also lowers the center of gravity of the snowmobile because of the lower positioning of the cylinder head, whereby it is possible to improve the maneuverability and travelling performance of the snowmobile. Further, the rear tilt arrangement of the engine creates a more space in front of the engine so that exhaust pipes and other components can be laid out with more flexibility, hence it is possible to further reduce the height of the engine hood. Since, if the intake system connected to the rear part of the engine is arranged over the engine the elements of the intake system can be arranged behind the headlight in the topmost portion of the engine hood, it is possible to improve the space efficiency without the need of modification or reconstruction such as increasing the height of the engine hood.
Further, it is possible to make use of the empty space behind the headlight at the topmost portion of the engine hood, in which the headlight and instrument panel are disposed, and to interpose part of the intake system in an efficient manner, whereby it is possible to make the shape of the engine hood short in its height.
In addition, exhaust can be discharged from the body bottom at the center with respect to the body width. That is, since exhaust noise from the body bottom can be dispersed to both sides and since the exhaust opening is located in the front body, the noise arises at a position away from the rider so that the exhaust noise will not be very harsh to the rider while travelling. Further, since the opening is located at the center of the body width, the exhaust noise during travelling will scatter equally to both sides, and since the opening is directed downwards, extra muffling effects from the snow surface and from the snow scattered by the steering ski-runners can be expected.
The layout of the exhaust pipe from the engine up to the muffler is inclined downward as it goes frontwards. That is, this arrangement compliments the engine hood configuration which lowers as it goes frontward to improve the aerodynamic performance.
It is also possible to mount the muffler within the engine hood without the necessity of taking a large space in the longitudinal direction.
Further, it is preferred that the four-cycle engine is mounted in the engine hood with the lengthwise center of the crankshaft off-centered to one side with respect to the center of the body width direction.
Since the clutch mechanism is arranged at one side of the engine and a battery is arranged at the other side in the engine hood, the weight balance with respect to the width direction can be easily adjusted.
It is also possible to adjust the weight balance in a more exact manner, by attaching electrical equipment such as an ECU, CDI unit to the battery holder. Further, since electrical equipment can be laid out next to the engine, it is possible to shorten their lead wires from the engine, hence simplify the routing of wires.
According to the present invention, the following effects can be further obtained.
Since, in a snowmobile, the engine is arranged in front of the steering post and an intake passage including an intake manifold and the like is disposed between the steering post and the engine body, it is possible to set the engine at the center of the snowmobile body.
Since air can be supplied to the intake manifold by downdraft ventilation by the arrangement of the intake passage at a position higher than the engine body, it is possible to receive air without being blocked by the engine and hence improve the air-cooling effect of the flow of air during travel. Further, since the intake manifold is arranged at the side of the steering post, it is possible to achieve a space-saving engine layout.
Further, the front body includes an instrument panel at the top thereof and an engine hood in front of the instrument panel, and the engine hood is formed so that it starts at a position stepped down a degree from the front end of the instrument panel toward the front end while a headlight facing outwards and frontwards is arranged at the stepped portion between the engine hood and instrument panel, and a throttle body as a carburetor is disposed in a space behind the headlight under the instrument panel inside the engine room. By this arrangement, it is possible to design the engine hood without any restriction of the engine height.
Since the engine is arranged with the axis of its crankshaft therein set approximately parallel to the body width direction while the throttle body is arranged at a level higher than the cylinder head, it is possible to receive air without being blocked by the engine and hence improve the air-cooling effect of the flow of air during travel.
Since the engine has an air cleaner box disposed at the rear of a head cover that covers the cylinder head and a first breather hose that connects the interior of the head cover with the interior of the air cleaner box, it is possible to return oil mist, water, etc., to the air cleaner box. Further, since the first breather hose is connected at one end to the rear side of the head cover on the drive-clutch side and is extended approximately linearly, and parallel to, the axial direction of the crankshaft, from the drive clutch side to the opposite side and bent perpendicularly, when viewed from top, and further extended and connected at the other end to the air cleaner box, no oil or water will stagnate within the first breather hose, so it is possible to prevent the freezing inside the intake passage.
Since, when the snowmobile body is in its horizontal position, the first breather hose is positioned so that its joint to the head cover is lower than its joint to the air cleaner box, there is no risk of oil leaking if the body is tilted during travelling or during stopping.
Further, since the engine has a second breather hose which connects the interior of the air cleaner box to the outside of the body, there is no risk of water stagnating within the intake passage including an air filter, intake pipe, carburetor and the like, hence it is possible to prevent freezing inside the intake passage. Further, since the second breather hose is connected at one end to the bottom of the air cleaner box while the other end is arranged penetrating through the bottom of the front body and opening to the outside, the water inside the air cleaner box can be drained to the outside of the snowmobile body, hence it is possible to prevent freezing inside the intake passage.